A conventional optical printer head with a light emitting diode array comprises a light emitting diode array chip mounted on a ceramic substrate, and a rod lens array (generally called by a trademark "SELFOC LENS ARRAY") for focusing exposure lights radiated from the light emitting diode array chip on a photosensitive medium of an optical printer. The light emitting diode array chip is driven in accordance with image signals read from an image memory by a driver integrated circuit which is also mounted on the ceramic substrate. The ceramic substrate is fixed to a base plate above which the rod lens array is held by fixing members. For this purpose, the rod lens array is fixed to the fixing members by use of eccentric screws.
In the optical printer head described above, an eccentric degree of the eccentric screws are adjusted when the rod lens array is fixed to the fixing members so that the rod lens array is positioned with a predetermined distance which is determined in accordance with focal lengths of rod lenses for the rod lens array from the light emitting surface of the light emitting diode array chip.
Further, a common line pattern for the light emitting diode array chip and a ground line pattern for the driver integrated circuit are provided on the ceramic substrate.
In operation, electric current of light emitting diodes which are driven in accordance with image signals is flowed from the light emitting diode array chip through the common line pattern to the ground, and electric current by which logic circuits in the driver integrated circuits are activated is flowed from the driver integrated circuit through the ground line pattern to the ground.
According to the conventional optical printer head, however, an eccentric degree of the eccentric screws are adjusted to minimize sizes of beam spots radiated from the light emitting diode array chip which are monitored when the rod lens array is fixed to the fixing members. For this reason, there is a disadvantage that a productivity of the optical printer head is decreased. Such a assembling procedure must be performed at each time of routine inspections or repairs of the optical printer head.
There is a further disadvantage that a distance between the rod lens array and the light emitting surface of the light emitting diode array chip is deviated off a predetermined distance due to the change of a temperature, vibrations and so on even if the rod lens array is fixed with the predetermined distance from the light emitting diode array chip because an eccentric screw is difficult to keep a predetermined fixing force for a long time.
There is a still further disadvantage that a printing mode in which all dots of a printing line are black is difficult to be conducted. This is a reason why electric current of 17 to 20A is flowed in the ground line pattern and the common line pattern when such a printing mode is performed so that a voltage drop of several volts is occured therein. As a result, normal operations are not expected to be performed in the light emitting diode array chip and the driver integrated circuit. In such an occasion, the aforementioned printing mode must be performed in such a manner that a printing line is divided into a predetermined number of groups which are printed sequentially. Otherwise, an extra power source 20 to 30 V must be prepared to print in the aforementioned printing mode. In a case where such a power source is provided therein, a circuit matching will be difficult to be made between the extra power source and remaining logic circuits nomally requiring a power source voltage of 5 V, and an evenness of printing densities is not kept because the difference of voltage drops is large between an input and output terminals of the ground and common line patterns. The ground and common line patterns are difficult to be thick to a desired extent thereby resulting in the decrease of resistance values because the patterns are normally provided with a thickness of 5 .mu.m by using the thin film process and with a thickness of 100 .mu.m by using the thick film process.